Cyclin-dependent kinases (CDKs) are serine/threonine protein kinases whose activity depends on binding and activation by cyclin partners. These heterodimeric complexes can phosphorylate various substrates involved in the control of transcription and cell-cycle progression in response to different stimuli. CDK8 and CDK9 have key roles in the control of transcription by RNA polymerase II. CDK9 responds specifically to several cytokines, including tumor necrosis factor and interleukin-6, indicating that it might have special roles in the regulation of a variety of physiological processes, especially immune responses, inflammation, cell activation, and differentiation.
Deregulated CDK activity is a hallmark of human cancer, and a variety of genetic and epigenetic events, such as over expression of cyclins, diminished levels of CDK inhibiting proteins or gain- of function mutations in CDK, have been described to cause increased activity of these enzymes and provide a selective growth advantage in tumor cells. CDK9 inhibition causes rapid depletion of short-lived mRNA transcripts and their associated protein products. Many genes encoding proteins involved in cell growth, proliferation, and tumor development (Myc, Cyclin D1, and Mcl-1) are characterized by short-lived mRNAs and proteins and hence the consequences of CDK9 inhibition include anti-proliferative and pro-apoptotic effects through loss of function at many cellular pathways. Tumor types that are dependent on labile pro-survival proteins (e.g., Mcl-1), which includes multiple myeloma, CLL, breast, melanoma and pancreatic cancers as well as the MYC-driven tumors (multiple cancer types) would be susceptible to CDK9 inhibition. CDK9 inhibitors might also be effective in combination with standard of care in tumors in which NF-κB is constitutively active and contributing to chemo resistance. This includes hematologic malignancies as well as solid tumors (breast, colorectal, prostate, melanoma and pancreatic). Thus, CDK9 inhibition targets multiple cancer-relevant pathways by inhibition of a single protein and thereby renders CDK9 as an attractive target for anti-cancer therapy. (Nature Reviews Cancer: 2009, 9, 153-166).
CDK9 inhibitors can also find therapeutic application in cardiology and virology as many viruses depend on the infected host for transcription of their genome. (Cyclin-dependent kinase 9: a key transcriptional regulator and potential drug target in oncology, virology and cardiology. Trends in Pharmacol. Sci. 2009, 29. 302-312; Pharmacological targeting of CDK9 in cardiac hypertrophy. Med Res. Rev. 2010 30:646-66; Novel HIV-1 therapeutics through targeting altered host cell pathways. Expert Opin Biol Ther. 2009 9:1369-82).
CDK9 inhibitors have also been reported as potential therapeutics for the treatment of chronic, inflammatory and neuropathic pain (WO2008/049856; WO2009/047359).
In view of the above, there is a need in the art for small molecule therapeutics that can inhibit the activity of CDK9. The present invention fulfills at least this need.